Raise for throwing errors in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to raise a RuntimeError with a message.

Ruby

raise [1], "Something went wrong!"

Drag options to blanks, or click blank then click option'

Athrow

Bcatch

CRuntimeError

Drescue

Attempts:

3 left

💡 Hint

Common Mistakes

Using throw or catch instead of an error class.

Omitting the error class and only writing raise.

The raise keyword is used to throw an exception. RuntimeError is a common error type to raise with a message.

2fill in blank

medium

Complete the code to raise a custom error with a message.

Ruby

class MyError < StandardError; end

raise [1], "Custom error occurred"

Drag options to blanks, or click blank then click option'

AMyError

BException

CError

DStandardError

Attempts:

3 left

💡 Hint

Common Mistakes

Using Exception or Error instead of the custom class.

Not defining the custom error class before raising it.

To raise a custom error, use the custom class name after raise. Here, MyError is the custom error class.

3fill in blank

hard

Fix the error in the code to correctly raise an ArgumentError with a message.

Ruby

raise ArgumentError [1] "Invalid argument!"

Drag options to blanks, or click blank then click option'

A,

B.

C:

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Using a dot or colon instead of a comma.

Omitting the separator between error class and message.

When raising an error with a message, separate the error class and message with a comma.

4fill in blank

hard

Complete the code to raise a ZeroDivisionError with a custom message.

Ruby

raise [1] , "Cannot divide by zero!"

Drag options to blanks, or click blank then click option'

AZeroDivisionError

BArgumentError

C,

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong error class like ArgumentError.

Using a dot instead of a comma to separate the message.

The error class ZeroDivisionError is raised with a message separated by a comma.

5fill in blank

hard

Fill all three blanks to raise a custom error with a message and rescue it.

Ruby

class [1] < StandardError; end

begin
  raise [2], "Oops!"
rescue [3] => e
  puts e.message
end

Drag options to blanks, or click blank then click option'

ACustomError

DStandardError

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the custom error class.

Rescuing a different error class than the one raised.

Define a custom error class CustomError, raise it, and rescue it by the same class to handle the error.

Practice

1. What does the raise keyword do in Ruby?

easy

A. It stops the program and throws an error.

B. It prints a message to the screen.

C. It creates a new variable.

D. It repeats a block of code.

Solution

1. Step 1: Understand the purpose of raise

   The raise keyword is used to stop the program and signal that an error has occurred.

2. Step 2: Compare with other options

   Printing messages, creating variables, or repeating code are not what raise does.

3. Final Answer:

   It stops the program and throws an error. -> Option A

4. Quick Check:

   raise stops program = D [OK]

Hint: Remember: raise means stop and show error [OK]

Common Mistakes:

• Thinking raise prints messages
• Confusing raise with loops
• Assuming raise creates variables

2. Which of the following is the correct syntax to raise a runtime error with a message in Ruby?

easy

A. raise "Error happened"

B. throw "Error happened"

C. error.raise("Error happened")

D. raise: "Error happened"

Solution

1. Step 1: Recall Ruby syntax for raising errors

   In Ruby, raise followed by a string message raises a RuntimeError with that message.

2. Step 2: Check each option

   raise "Error happened" uses correct syntax. throw "Error happened" uses throw which is different. error.raise("Error happened") is invalid method call. raise: "Error happened" has wrong colon usage.

3. Final Answer:

   raise "Error happened" -> Option A

4. Quick Check:

   Correct raise syntax = A [OK]

Hint: Use raise followed by message in quotes [OK]

Common Mistakes:

• Using throw instead of raise
• Adding colon after raise
• Calling raise as a method on error

3. What will be the output of this Ruby code?

def check_age(age)
  raise "Age must be 18 or older" if age < 18
  "Access granted"
end

puts check_age(20)

medium

A. Age must be 18 or older

B. No output

C. RuntimeError: Age must be 18 or older

D. Access granted

Solution

1. Step 1: Analyze the condition in the method

   The method raises an error only if age is less than 18. Here, age is 20, so no error is raised.

2. Step 2: Determine the returned value and output

   Since no error is raised, the method returns "Access granted" which is printed by puts.

3. Final Answer:

   Access granted -> Option D

4. Quick Check:

   Age 20 >= 18, no error = B [OK]

Hint: Raise only triggers if condition is true [OK]

Common Mistakes:

• Assuming error always raises
• Confusing error message with output
• Ignoring the if condition

4. Identify the error in this Ruby code snippet:

def divide(a, b)
  raise "Cannot divide by zero" if b = 0
  a / b
end

puts divide(10, 0)

medium

A. Division operator is incorrect

B. Missing parentheses in raise statement

C. Using assignment (=) instead of comparison (==) in the if condition

D. Method divide is not defined

Solution

1. Step 1: Check the if condition syntax

   The condition uses b = 0 which assigns 0 to b instead of comparing it. This is a common mistake.

2. Step 2: Understand the impact

   Because of assignment, b becomes 0, and since 0 is falsy in Ruby, the condition evaluates to false, so the raise is not triggered. The intended check is b == 0.

3. Final Answer:

   Using assignment (=) instead of comparison (==) in the if condition -> Option C

4. Quick Check:

   Use == for comparison, not = [OK]

Hint: Use == to compare, not = which assigns [OK]

Common Mistakes:

• Confusing = and ==
• Thinking raise needs parentheses
• Assuming divide method is missing

5. You want to raise a custom error type ArgumentError with a message "Invalid input" when a method receives a negative number. Which code correctly does this?

hard

A. ArgumentError.raise("Invalid input") if number < 0

B. raise ArgumentError, "Invalid input" if number < 0

C. raise "ArgumentError: Invalid input" if number < 0

D. raise ArgumentError("Invalid input") if number < 0

Solution

1. Step 1: Understand how to raise custom error types

   In Ruby, you can raise a specific error class by passing it as the first argument to raise, followed by the message.

2. Step 2: Check each option's syntax

   raise ArgumentError, "Invalid input" if number < 0 correctly uses raise ArgumentError, "Invalid input". raise "ArgumentError: Invalid input" if number < 0 treats the error as a string only. ArgumentError.raise("Invalid input") if number < 0 is invalid as raise is not a method on ArgumentError. raise ArgumentError("Invalid input") if number < 0 is invalid syntax.

3. Final Answer:

   raise ArgumentError, "Invalid input" if number < 0 -> Option B

4. Quick Check:

   Raise with error class and message = C [OK]

Hint: Use raise ErrorClass, "message" for custom errors [OK]

Common Mistakes:

• Passing error as string only
• Using wrong syntax with parentheses
• Confusing new method call with raise